1. Field of the Invention
The present invention relates to a process for the emulsion polymerization of one or more olefins by reacting a ligand of the formula Ia or Ib or a mixture of at least two of the ligands Ia or Ib
in each of which R denotes one or more of the following radicals:    hydrogen    halogen    nitrile    C1-C12 alkyl, C1-C12 alkoxy, C7-C13 aralkyl, C6-C14 aryl groups, unsubstituted or substituted by: C1-C12 alkyl groups, halogens, C1-C12 alkoxy, C3-C12 cycloalkyl, C1-C12 thioether groups, carboxyl groups or sulfo groups present where appropriate in the form of their salts, and also amino groups with hydrogen and/or C1-C12 alkyl radicals    amino groups NR1R2, where R1 and R2 together or separately are hydrogen, C1-C12 alkyl, C7-C13 aralkyl or C6-C14 aryl groups and may additionally form a saturated or unsaturated 5- to 10-membered ring, unsubstituted or substituted by: C1-C12 alkyl groups, halogens, C1-C12 alkoxy, C3-C12 cycloalkyl, C1-C12 thioether groups, carboxyl groups or sulfo groups present where appropriate in the form of their salts, and also amino groups with hydrogen and/or C1-C12 alkyl radicals    and where identical or different compounds of the formulae Ia and Ib may where appropriate also be bridged by one or more C1-C12 alkylene, C2-C12 alkylated azo or formula II bridges
    where Y is silicon or germanium and R3 and R4 are hydrogen and/or C1-C12 alkyl,    with a phosphine compound PR′3, where R′ is hydrogen, C1-C12 alkyl, C4-C12 cycloalkyl, C7-C15 aralkyl or C6-C15 aryl groups,    or with a diphosphine compound R′2P-G-PR′2, where R′ is as defined for the phosphine compounds PR′3 and G is C1-C12 alkyl, C4-C12 cycloalkyl, C7-C15 aralkyl or C6-C15 aryl groups,    and also with a metal compound of the formula M(L2)2 or M(L2)2(L1)z,where the variables are defined as follows:    M is a transition metal from groups 7 to 10 of the Periodic System of the Elements;    L1 is phosphanes (R5)xPH3-x or amines (R5)xNH3-x with identical or different radicals R5, ethers (R5)2O, H2O, alcohols (R5)OH, pyridine, pyridine derivatives of the formula C5H5-x(R5)xN, CO, C1-C12 alkyl nitrites, C6-C14 aryl nitriles or ethylenically unsaturated double bond systems, x being an integer from 0 to 3,    R5 is hydrogen, C1-C20 alkyl groups, which may in turn be substituted by O(C1-C6 alkyl) or N(C1-C6 alkyl)2 groups, C3-C12 cycloalkyl groups, C7-C13 aralkyl radicals, and C6-C14 aryl groups,    L2 is halide ions, R6xNH3-x, where x is an integer from 0 to 3 and R6 is C1-C12 alkyl, and also C1-C6 alkyl anions, allyl anions, benzyl anions or aryl anions, it being possible for L1 and L2 to be linked to one another by one or more covalent bonds,    z is a number from 0 to 4,and using the reaction product immediately to polymerize or copolymerize olefins in water or a solvent mixture with a water content of at least 50% by volume in the presence of an emulsifier and, optionally, of an activator.
The complex formed in situ does not undergo isolation and purification.
For the process of the invention it is optional to use an activator such as, for example, olefin complexes of rhodium or of nickel. This invention further relates to dispersions of polyolefins such as polyethylene and ethylene copolymers in water, to the use of the aqueous dispersions of the invention for paper applications such as paper coating or surface sizing, paints, adhesive base materials, foam moldings such as mattresses, applications to textiles and leather, coatings on carpet backings, or pharmaceutical applications.
2. Description of the Background
Aqueous dispersions of polymers are utilized commercially in numerous, very different applications. Examples include paper applications (coating and surface sizing), base materials for paints and varnishes, adhesive base materials (including pressure sensitive adhesives), applications to textiles and leather, chemicals used in the construction industry, foam moldings (mattresses, coatings for carpet backings), and also for medical and pharmaceutical products, as binders for preparations, for example. A summary can be found in D. Distler (editor) “WäBrige Polymerdispersionen”, Wiley-VCH Verlag, 1st edition, 1999.
To date it has been difficult to prepare aqueous dispersions of polyolefins. It would, however, be desirable to be able to prepare such aqueous dispersions of polyolefins, since the monomers such as ethylene or propylene are very advantageous from an economic standpoint.
The commonplace processes for preparing such aqueous dispersions from the corresponding olefins make use either of free-radical high-pressure polymerization or else of the preparation of secondary dispersions. These processes are hampered by disadvantages. The free-radical polymerization processes require extremely high pressures, are restricted to ethylene and ethylene copolymers on the industrial scale, and involve an apparatus which is very expensive to purchase and maintain. Another possibility is first to polymerize ethylene, by any desired process, and then to prepare a secondary dispersion, as described in U.S. Pat. No. 5,574,091. This method is a multistage process and hence is very cumbersome.
It is therefore desirable to polymerize 1-olefins such as ethylene or propylene under the conditions of emulsion polymerization and to prepare the required dispersion in one step from the corresponding monomer. Moreover, emulsion polymerization processes have the advantage, very generally, that they give polymers of high molar mass, the removal of heat being easy to manage as an inherent feature of the process. Lastly, reactions in aqueous systems very generally are of interest, on account of the fact that water is an inexpensive and environmentally friendly solvent.
Processes proposed to date for the emulsion polymerization of 1-olefins such as ethylene or propylene require further improvement. The problem generally resides in the catalyst which is needed to polymerize these monomers.
With electrophilic transition metal compounds such as TiCl4 (Ziegler-Natta catalyst) or metallocenes it is possible to polymerize olefins, as described, for example, by H.-H. Brintzinger et al. in Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. However, both TiCl4 and metallocenes are sensitive to moisture and are therefore poorly suited to preparing polyolefins in emulsion polymerization. The aluminum alkyl cocatalysts used are also sensitive to moisture; accordingly, water, as a catalyst poison, must be carefully excluded.
There are but few reports of transition metal catalyzed reactions of ethylene in aqueous medium. For instance, L. Wang et al. in J. Am. Chem. Soc. 1993, 115, 6999 report a rhodium catalyzed polymerization. At around one insertion per hour, however, the activity is much too low for industrial applications.
The reaction of ethylene with nickel-P,O-chelate complexes appears much more promising, as it is described in U.S. patents U.S. Pat. No. 3,635,937 and U.S. Pat. No. 3,686,159. The polymer analysis data are not reported. Additionally, the reported activity is still much too low for industrial applications.
EP-A 0 046 331 and EP-A 0 046 328 report the reaction of ethylene with Ni-chelate complexes of the formula A
where R refers to identical or different organic substituents of which one carries a sulfonyl group and F denotes phosphorus, arsenic or nitrogen. The selected reaction conditions in solvents such as methanol or mixtures of methanol and a hydrocarbon produced only oligomers, which are not suitable for the applications specified above.
U.S. Pat. No. 4,698,403 (column 7, lines 13-18) and U.S. Pat. No. 4,716,205 (column 6, lines 59-64) show that an excess of water acts as a catalyst poison to bidentate Ni-chelate complexes, even when they carry an SO3− group.
From the documents cited above it is apparent that numerous Ni complexes are not active in polymerization in the presence of water.
Furthermore, WO 97/17380 discloses that palladium compounds of the formula B
where R′ stands, for example, for isopropyl groups, or the analogous nickel compounds, are able to polymerize higher olefins such as 1-octene in an aqueous environment. An option is to add an emulsifier, in order to facilitate the polymerization. Nevertheless, it is specified that the temperature of 40° C. should not be exceeded, since otherwise the catalyst is deactivated (p. 25, lines 5 et seq.). Higher reaction temperatures, however, are generally desirable, since they allow the activity of a catalyst system to be increased.
Further drawbacks of formula B catalyst systems are that, with ethylene, highly branched polymers are generally formed (L. K. Johnson, J. Am. Chem. Soc. 1995, 117, 6414), which have been of little significance industrially to date, and that, with higher α-olefins, the phenomenon known as “chain running” is inevitably observed in the active complexes. Chain running leads to a large number of 1,ω-misinsertions, as a result of which, generally, amorphous polymers are produced, which are poorly suited to use as materials of construction.
It is also known that complexes of the formula C
(WO 98/42665), where M=Ni or Pd, having n neutral ligands L, are active in polymerization in the presence of small amounts of water without detriment to the catalytic activity (page 16, line 13). These amounts of water, however, must not exceed 100 equivalents, based on the complex (page 16, lines 30-31). Under these conditions, though, it is impossible to carry out an emulsion polymerization.
It is disclosed, moreover, that complexes of the formula D
having identical or different radicals R are capable of polymerizing ethylene in the presence of small amounts of water (WO 98/42664, especially page 17, lines 14 et seq.). These amounts of water, however, must not exceed 100 equivalents, based on the complex (page 17, lines 33-35). Under these conditions, though, it is impossible to carry out an emulsion polymerization.
The preparation of aqueous dispersions with the aid of transition metal catalysts is also described in EP-A 1110977 and WO 01/44325.
Furthermore, the two laid-open specifications DE-A 2923206 and DE-A 3345785 each describe processes for preparing polyethylene using catalysts referred to as in situ catalysts, consisting of a nickel compound and a mixture of a quinonoid compound and also a tertiary phosphine. Neither of these documents, however, discloses that these catalysts can be used to prepare aqueous dispersions containing polyethylene.
In view of the great commercial importance of polyolefins, the search for improved processes for polymerization continues to be of great importance.